196 



either covers the sporangium on all sides (having the shape of a 

 bell), or is split on one side (Fig. 200 jB, 7i). 



Among peculiar forms may be mentioned : Splachnum, which is especially 

 remarkable for the collar-like expansion at the base of the capsule. Fissidens 



deviates in having a flat stern and leaves 

 arranged in two rows. The leaves are 



I boat-shaped and half embrace the stem. 



Schistoatega has two kinds of sterns. 

 The barren ones resemble Fern-leaves ; 

 they have two rows of leaves, which are 

 attached together vertically, are decur- 

 rent, and coalesce at their bases. The 

 fertile ones have an ordinary appearance. 

 Tetraphis : the peristome is composed 

 of four teeth, wbich are formed from entire 

 cells. 2'. pellucida has peculiar gemmae. 



The family is divided into two 

 groups : the Musci acrocarpi, the 

 growth of whose main axis is 

 limited and terminated by the 

 formation of the sexual organs ; 

 and the Musoi pleurocarpi, whose 

 sporogonia are situated on special 

 lateral shoots, while the growth of 

 the main axis is unlimited. 



FIG. 200. A Hypnum populeum. B 

 and C Sporangia, with hood (h), and 

 operculum (!'), and without these (C), 

 showing the peristome (p). D The 

 mouth of the capsule of Fonfinalis ant-i- 

 pyretica. 



A. Acrocarpi. 



Order 1. Weisiaceae. Peristome, 

 with 16 teeth arranged in one series, rarely 

 wanting. Leaf with midrib. Campy lopus, 

 Dicranum (D. scoparium, common in forests), Dicranella, Cynodontium. 

 Weisia, Gymnostomum (no peristome), Systegium. 



Order 2. Leucobryaceae. Peristome with 16 teeth. Leaves with three or 

 more layers of cells, of which the external ones are air-conducting and per- 

 forated (as in the Sphagneas), the middle one containing chlorophyll. Leuco- 

 bryum. 



Order 3. Fissidentaceas. Peristome as in the preceding ones. The 

 leaves are arranged in two rows on the plagiotropic shoots ; in Fissidens the 

 midrib of the leaf bears wing-shaped outgrowths. Conomitrium, Fissidens. 



Order 4. Seligeriaceaa. Peristome with 16 undivided teeth. Very small 

 Hock-mosses. Seligeria. Blindia. 



Order 5. Pottiacese. Peristome with 16 teeth, which are divided almost 

 to the base, or with 32 teeth. Calyptra hood-like. Barbula (B. muralis, B. 

 raralis), Trichostomum, Leptotrichiiin. Ceratodon pnrpureus. Distichium. 

 Pottia. 



